I know I posted them, but I personally believe the Jimmy Hopkins ones are bull tbh. I think people just made certain things up that are Rockstar-related to get people suckered into wasting time and looking for something that isn't there (Bigfoot, Lola, UFO's etc)

If you steal one of the modded Sentinels you can see in it's spoiler that it reads "STD- Sentinel Tuning Division".
Other than being a reference to the Sexually Transmitted Diseases it's a spoof of Toyota's TRD(Toyota Racing Development).

47. Mastibating Statue
If you go to the National Union of Contemporary Arts(NUCA; it's about a block east from Steinway Beer Garden) you will find a "masterpiece" made with blocks that resembles a guy masturbating. Also one of the statues that is covered is obviously flipping the bird.
Found by J-Star &oXReapeRXo

The one with the covered statue is in another place, the gallery at Middle Park(Smithsonian spoof).